1. Field of the Invention
The present invention relates to a process of producing a water absorptive resin.
2. Discussion of the Prior Art
It is well known that a cross-linked water-soluble polymer such as poly(sodium acrylate) or sodium polyacrylate changes from a water-soluble resin to a water-insoluble resin as the cross linking density of the polymer increases. As a typical example of such cross-linked water-soluble polymer, there is known cross-linked sodium polyacrylate which is obtained by copolymerizing a sodium acrylate monomer with a cross-linking agent such as methylenebis (acrylamide). This cross-linked sodium polyacrylate is widely used in various fields, as a water absorptive polymer which has high water absorbing capability.
While the cross-linked sodium polyacrylate has a considerable hygroscopic swelling property, the rate or velocity of water absorption is relatively low, particularly for seawater or saltwater. This low water absorption rate is an obstacle to the practical application of the sodium polyacrylate, for example, as a water cut-off material for an optical fiber cable where the cable is a submarine cable. For this application, therefore, there is a need for improving the rate at which the cross-linked sodium polyacrylate absorbs water, in particular, seawater.